Methicillin-Resistant Staphylococcus Aureus is a type of bacteria that are resistant to certain types of antibiotics. It has become a serious public health threat because it is both widespread and highly contagious.
The length and difficult pronunciation of the medical phrase Methicillin-Resistant Staphylococcus Aureus, has led most people to refer to the condition by its four-letter acronym MRSA. However, MRSA is typically pronounced mersa which has created some confusion as to the proper term to use.
Although MRSA is the technically correct abbreviation for methicillin-resistant staphylococcus aureus, MERSA has become widely accepted and understood as well.
In conversation, the difference between MRSA and MERSA is, of course, irrelevant since pronunciation is the same. Where the distinction may be important is when searching for relevant information and materials on the internet.
For example, a search for "MERSA" on Google US Government Search (http://www.google.com/unclesam) returns no relevant links in the first 10 search results. A search for "MRSA", on the other hand, returns all highly relevant results from respected authoritative government sources like the Centers for Disease Control and the national Institutes of Health.